It may not be against the TOS, but playing xbox through your broadband card will sure go over the 5bg monthly cap - so they'ed cancel your account anyway.
BTW - VZW does not offer an "unlimited" broadband plan anymore. Actually, they never did. Funny how getting sued will make you correct the language you use.
Logically, it would be more adequate for usage of an xbox 360 of pc gaming to have a wired connection or atleast to play off a wireless router. To play off the air card itself will not suffice in the speed and moreover will not be as cost effective as playing off a wireless or wired connection through your home.
Mobile broadband is intended for it's convenience of having a stable connnection when and if you are traveling. It is not necessarily intended to be used as dedicated home connection for gaming usage.
I just got broadband wireless for my computer about a month ago, and it's alot faster than dial-up. I cannot believe the connection
speed tht i get with broadband.. I will never go back to dial-up. And i would tell friends tht don't have dsl,fios to get the broadband